In distribution of movie content in recent years, the number of streams multiplexed to form one digital stream is on the increase. In view of this, the stream selection function mentioned above is regarded as particularly important. The increase in the number of streams is due to an attempt to support every combination of codec, channel number, and language attribute.
Suppose there are three codecs AC-3 (2ch), AC-3 (5.1ch), and DTS (5.1ch), and two language attributes Japanese and English. In this case, six audio streams corresponding to six combinations of these codecs and language attributes are produced and multiplexed to form one digital stream. These audio streams have a specific numbering system. Accordingly, by setting a stream number of one of the audio streams in a status register in a playback apparatus so that the playback apparatus selects the audio stream identified by the stream number in the status register, the audio stream corresponding to the particular codec-language combination can be played at each playback session.
The status register used here is initialized upon factory shipment, and may be updated later by the user.
In the above playback apparatus, the status register is unchanged unless the user updates it. This being so, once the status register has been set to indicate, for example, AC-3 (2ch), even when content includes an AC-3 (5.1ch) audio stream, the AC-3 (5.1ch) audio stream is not played unless the user updates the status register. In this case, the AC-3 (5.1ch) audio stream is wasted. To avoid this, it may be suggested to provide the playback apparatus with a function of automatically setting the status register so as to utilize its AC-3 (5.1ch) playback capability.
However, not every content contains an AC-3 (5.1ch) audio stream. For example, an AC-3 (5.1ch) audio stream is certainly included in content of a recent hit movie, but may not be included in content of an old movie or an art film. If the status register automatic setting function operates when playing content that does not include an AC-3 (5.1ch) audio stream, the playback apparatus will end up selecting a nonexistent audio stream.
Conversely, it may be suggested to store, on a BD-ROM carrying an AC-3 (5.1ch) audio stream, information for automatically selecting the AC-3 (5.1ch) audio stream. However, not every playback apparatus has an AC-3 (5.1ch) decoding capability. If the BD-ROM instructs a playback apparatus without the AC-3 (5.1ch) decoding capability to select the AC-3 (5.1ch) audio stream, a problem occurs.
Thus, since not every content includes an AC-3 (5.1ch) audio stream and not every playback apparatus has an AC-3 (5.1ch) decoding capability, the user needs to set the status register in order to select an optimal audio stream at each playback session. A failure to do so often causes an AC-3 (5.1ch) audio stream to be wasted without being played back.